This invention relates generally to the cryogenic separation of feed air for the production of nitrogen and, more particularly, to an improved plant for the production of same.
In the production of nitrogen by the cryogenic rectification of feed air, the feed air, after being pressurized and cleaned of high boiling impurities, undergoes cooling to the proper temperature prior to being introduced into a cryogenic rectification column. Fluids from the column undergo one or more subcooling, condensation, vaporization and heating steps, and the product nitrogen is heated prior to recovery. These separation and heat exchange operations require the use of an extensive piping network as fluids are passed from one piece of equipment to another in order to carry out these operations. Such a network is complicated, expensive to construct, and inefficient to operate. A cryogenic nitrogen production plant which reduces the complexity of heretofore necessary piping networks would be highly desirable.
Accordingly, it is an object of this invention to provide a cryogenic nitrogen production plant which for comparable production capability is less complex than heretofore available cryogenic nitrogen production plants.
The above and other objects, which will become apparent to one skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
Apparatus for producing product nitrogen by the cryogenic separation of feed air comprising:
(A) a brazement containing a heat exchange section, a condenser, and a separation section;
(B) means for passing feed air from outside the brazement into the heat exchange section, and means for passing feed air from the heat exchange section to the separation section;
(C) means for passing waste fluid from the separation section to the condenser, means for passing waste fluid from the condenser to the heat exchange section, and means for passing waste fluid from the heat exchange section to outside the brazement; and
(D) means for passing product nitrogen from the separation section to the heat exchange section, and means for passing product nitrogen from the heat exchange section to outside the brazement for recovery.
Another aspect of the invention is:
Apparatus for producing product nitrogen by the cryogenic separation of feed air comprising:
(A) a brazement containing a heat exchange section and a condenser, and a separation section outside of the brazement;
(B) means for passing feed air from outside the brazement into the heat exchange section, and means for passing feed air from the heat exchange section to the separation section;
(C) means for passing waste fluid from the separation section to the condenser, means for passing waste fluid from the condenser to the heat exchange section, and means for passing waste fluid from the heat exchange section to outside the brazement; and
(D) means for passing product nitrogen from the separation section to the heat exchange section, and means for passing product nitrogen from the heat exchange section to outside the brazement for recovery.
As used herein, the term xe2x80x9cfeed airxe2x80x9d means a mixture comprising primarily nitrogen and oxygen, such as ambient air.
As used herein, the term xe2x80x9cturboexpansionxe2x80x9d and xe2x80x9cturboexpanderxe2x80x9d mean respectively method and apparatus for the flow of high pressure gas through a turbine to reduce the pressure and the temperature of the gas thereby generating refrigeration.
As used herein, the term xe2x80x9ccolumnxe2x80x9d means a distillation of fractionation column or zone, i.e. a contacting column or zone wherein liquid and vapor phases are counter currently contacted to effect separation of a fluid mixture, as for example, by contacting or the vapor and liquid phases on a series of vertically spaced trays or plates mounted within the column and/or on packing elements which may be structured packing and/or random packing elements. For a further discussion of distillation columns, see the Chemical Engineer""s Handbook fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13, The Continuous Distillation Process. 
Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phase is adiabatic and can include integral or differential contact between the phases. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin.
As used herein, the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9csubcoolxe2x80x9d means to cool a liquid to be at a temperature lower than the saturation temperature of that liquid for the existing pressure.
As used herein, the term xe2x80x9cphase separatorxe2x80x9d means a vessel wherein incoming feed is separated into individual vapor and liquid fractions. Typically, the vessel has sufficient cross-sectional area so that the vapor and liquid are separated by gravity.
As used herein, the term xe2x80x9cproduct nitrogenxe2x80x9d means a fluid having a nitrogen concentration of at least 90 mole percent.
As used herein, the term xe2x80x9cwaste fluidxe2x80x9d means a fluid having a nitrogen concentration which is less than the nitrogen concentration of the product nitrogen produced using the invention.
As used herein, the term xe2x80x9cbrazementxe2x80x9d means a structure for carrying out heat and/or mass transfer processes having a complex internal arrangement and being put together by brazing, soldering, welding and/or flange connections.
As used herein, the term xe2x80x9ccondenserxe2x80x9d means a device which generates reflux for use in cryogenic rectification.
As used herein, the term xe2x80x9creflux condenserxe2x80x9d means a structure that enables simultaneous heat and mass transfer while condensing a vapor.